Observation of living tissue by an endoscope includes, in addition to normal endoscopic observation using visible light, fluorescence observation in which fluorescence pictures are observed by irradiating excitation light. The fluorescence observation utilizes a characteristic in which, when light (excitation light) whose wavelength falls within 400 nm to 480 nm is irradiated to living tissue, normal tissue intensely emits fluorescence in the range of approximately 480 nm to 630 nm while fluorescence from diseased parts such as carcinoma cells is weaker, and is known as a technique that enables discovery of abnormal regions such as early cancer that are difficult to view under normal endoscopic observation.
Conventionally, as disclosed in Japanese Patent Laid-Open No. 4-150845, in an endoscope apparatus used in fluorescence observation, an excitation filter that transmits only excitation light is positioned in a path of illumination light emitted from a light source, and at the same time, a fluorescence transmitting filter that transmits only light having a fluorescence wavelength is positioned between an objective optical system at a distal end of an insertion portion of the endoscope and a solid state image pickup device.
With a conventional apparatus such as that disclosed in Japanese Patent Laid-Open No. 4-150845, illumination light irradiating a subject is limited to excitation light and light beams incident to the solid state image pickup device is limited to fluorescence. Consequently, the conventional apparatus becomes an apparatus dedicated to fluorescence observation which is incapable of performing endoscopic observation on the subject under normal light.
Therefore, conventionally, every time an endoscopic observation is performed in order to visually observe positions or conditions of a diseased part, it is required that an endoscope apparatus for fluorescence observation be replaced with an endoscope apparatus for normal light observation and vice versa for alternate use, thereby placing a heavy burden on both patients and doctors.
In consideration thereof for example, in Japanese Patent Laid-Open No. 9-066023, a video processor apparatus involving an electronic endoscope for fluorescence observation is proposed which is capable of readily performing both normal endoscopic observation and fluorescence observation. However, with such an apparatus, although both a normal light observation image and a fluorescence observation image are displayable on a monitor, a normal light observation image and a fluorescence observation image picked up at the same timing cannot be observed simultaneously. This creates a problem in that it is difficult to compare a normal light observation image and a fluorescence observation image, such as, for example, the same region cannot be observed when a subject moves during switching of observation images.
In addition, another problem exists in that, when displaying both a normal light observation image and a fluorescence observation image on the monitor, a state in which one of the images changes to a noise image or a state in which nothing is outputted occurs in the event that either a normal light observation CCD or a fluorescence observation CCD has a trouble, making it difficult to recognize on the monitor screen which CCD has a trouble.
Moreover, in addition to normal observation and fluorescence observation described above, observation of living tissue using an endoscope apparatus includes Narrow Band Imaging (NBI) in which narrowband light that is light whose band is narrower than that of illumination light used in normal observation is irradiated in vivo to perform observation, and infrared observation in which near-infrared light that is light having a near-infrared band is irradiated in vivo to perform observation.
Narrow Band Imaging enables observation of vessels in a superficial portion of mucous membrane at a higher contrast, while infrared observation enables observation of hemodynamics in submucous deep regions not viewable through normal observation by intravascular injection of an agent called indocyanine green (ICG) which absorbs near-infrared light.
Such an apparatus that enables switching among a plurality of observation modes is disclosed in, for example, Japanese Patent Laid-Open No. 2005-013611 as an image processing apparatus capable of switching among four observation modes, namely, normal observation, fluorescence observation, Narrow Band Imaging and infrared observation.
However, with fluorescence observation, since autofluorescence emitted by living tissue in vivo is weak, pickup of pictures under autofluorescence emitted by living tissue in vivo is performed by, for example, reducing the rotation speed of a rotary filter provided at a light source in comparison to normal observation in order to extend exposure time in comparison to normal observation.
Therefore, for example, during a time period in which the observation mode of an endoscope apparatus switches from normal observation to fluorescence observation or, in other words, during a time period in which the rotation speed of the rotary filter changes from a rotation speed suitable for normal observation to a rotation speed suitable for fluorescence observation, a problem arises in that a still image unsuitable for storing is outputted. Such a problem is not considered in Japanese Patent Laid-Open No. 2005-013611.
The present invention has been made in consideration of the above circumstances, and has as its object to provide an endoscope apparatus capable of readily comparing an normal light observation image and a fluorescence observation image and notifying an malfunction in an image processing system on the monitor, and to provide an image processing apparatus capable of outputting a still image suitable for storing when switching among observation modes is being performed.